Various CVD (Chemical Vapor Deposition) apparatuses are used for manufacturing electronic devices, such as semiconductor devices, LCD (Liquid Crystal Display) devices, etc. Plasma CVD apparatuses are widely used for forming high quality films.
The plasma CVD apparatus forms a film on a semiconductor wafer contained inside a decompressed chamber, using a CVD method. The CVD method employs a gas phase reaction. Thus, films are formed only on the surface of the wafers, but on the surface (internal wall, etc.) of a chamber member. Thus formed films cause particles to be generated, thereby lowering the yield of the products. In such circumstances, it is necessary to regularly clean the inside of the chamber, to remove the films formed on the chamber member.
A well-known method for cleaning the inside of the chamber is an in-situ plasma cleaning method, wherein a cleaning gas is introduced into the chamber, and plasma is generated from a gas inside the chamber. However, plasma is generated inside the chamber, so that the chamber member is likely to be deteriorated.
A remote plasma cleaning method has been proposed. In this remote plasma cleaning method, plasma of a cleaning gas is generated outside the chamber, and the generated plasma is introduced into the chamber so as to clean the inside of the chamber. Using this remote plasma cleaning method, the chamber member is unlikely to be deteriorated. Such a remote plasma cleaning method is disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H9-69504 (U.S. Priority No. 08/278605).
In the cleaning of the chamber using plasma, it is important to obtain an accurate end point of the cleaning, since the reactivity of plasma is high. Insufficient cleaning of the chamber causes particles to be generated, while excessive cleaning causes the chamber member to be deteriorated.
Conventionally, in the remote plasma cleaning method, the end point of cleaning had been estimated, based on the cleaning rate obtained in advance by carrying out some experiment. However, in this cleaning method, the actual cleanness inside the chamber is not measured. Hence, the end point of cleaning used above does not have high accuracy. The plasma cleaning using inaccurate end point causes the insufficient or excessive cleaning of the chamber, and thereby lowering the productivity of the CVD apparatus. Accordingly, in the conventional remote plasma cleaning, it is difficult to obtain the accurate end point of cleaning, so that it is difficult to obtain sufficiently high productivity of the CVD apparatus.